I don't believe that the MPG reading that shows up on the dash is for the entire duration of the ride (AUTO mode). The MPG changes way too rapidly even after a long time and distance, telling me that there is some finite distance or fuel usage for this measurement.

If it were for the entire duration, the MPG would come to a fairly steady reading and not change as frequently as it does.

Anyone have a clue about this???

 

It should average until you re-set it to zero. It should average multiple tanks of fuel if you wish. Trip B can calculate over multiple tanks even if you re-set Trip A to zero each tank. Doing this should answer your question actually.

 

No. If I travel a long distance in a single trip, the gas mileage should hardly ever change by the end of the trip. This is not the case, indicating to me that the MPG that's being displayed is only for the last couple of miles or less. Maybe it's for the amount of distance that it takes to get the FIRST MPG reading. What's that, about a half mile or so?

BTW, AUTO mode resets at every car start.

 

Which model and year do you have? I do not have, correction, I do have an "auto" mode on my base '09.

I have now selected this and will see what my mpg display does. The Owner's Handbook says it displays average fuel consumption between ignition events when set to "auto". Yours seems to be doing something else.

For Trip A and B my mpg display (liters/100km in my Canadian spec car) displays average fuel consumption since the last re-set. Other cars I have also show current instantaneous fuel consumption as an optional display but not my XF.

If yours does not read correctly then a trip to the dealer seems in order

 

2011 xfr

 

I have a US spec 2010 XF Premium and Auto behaves as Jagular describes. Maybe they have changed the software for the 2011?

 

My "auto" function accords almost exactly with Trip A and B. I conclude that it measures fuel consumption as a moving average. The exact number depends on the driving conditions over the measured period ie between resets.

If yours does not then either jaguar changed it or yours is defective.

 

It seems to me the Auto function aggregates from engine start.

Starting a long drive with conservative acceleration throughout yields a continually refined average, but driving aggressively for the last few miles doesn't affect the total average all that much. Example of a 25MPG average on a 40 mile commute, and the last few miles driving hard, the average mileage doesn't dip too far below the 25, but during that period, the real-time mileage is probably more like 15.

Conversely, driving very aggressively at the onset of a commute, then moving to a more conservative pedal will still result in the 25MPG by the end of the ride.

Based on these observations, I would have to say Auto continually adjusts throughout the run.